CHAOBORUS PREDATION AND SEX-SPECIFIC MORTALITY IN A COPEPOD

The susceptibility to Chaoborus predation in males and in females with and without eggs of the freshwater copepod Eudiaptomus gracilis was s tudied in held enclosures and by videotaping and analyzing the predati on cycle in the laboratory. Female mortality exceeded male mortality b oth in the field and in the laboratory. Chaoborus predation may theref ore contribute to skewed adult sex ratios in diaptomid populations. Cl utch size and the frequency of females carrying eggs was higher in pre dator-exposed field populations, but this may have been an indirect ef fect of a higher phytoplankton standing stock. There was no mortality difference between females with and without eggs in the laboratory. Th e attack rate did not differ between prey types, and all captured prey were ingested. The lower male mortality was due to a significantly lo wer efficiency in strikes directed against them. Analysis of the attac k events revealed that swimming angle of prey in relation to the Chaob orus larvae affected the probability of being captured. Differences in escape ability, size, and morphology may also contribute to the sex-s pecific mortality.